Method for forming bodies by reactive infiltration

ABSTRACT

This invention relates to a method for producing a self-supporting body comprising the steps of: 
     (a) forming a permeable mass comprising at least one solid-phase oxidant selected from the group consisting of the halogens, sulphur and its compounds, metals, metal oxides other than the silicates, and metal nitrides other than those of boron and silicon; 
     (b) orienting said permeable mass and a source of said parent metal relative to each other so that formation of said oxidation reaction product will occur into said permeable mass; 
     (c) heating said source of parent metal to a temperature above the melting point of said parent metal but below the melting point of said oxidation reaction product to form a body of molten parent metal; 
     (d) reacting said body of molten parent metal with said at least one solid-phase oxidant at said temperature to permit said oxidant at said temperature to permit said oxidation reaction product to form; and 
     (e) maintaining at least a portion of said at least one oxidation reaction product in contact with and between said molten parent metal and said solid-phase oxidant at said temperature to progressively draw molten parent metal through said oxidation reaction product towards said solid-phase oxidant to permit fresh oxidation reaction product to continue to form at an interface between said solid-phase oxidant and previously formed oxidation reaction product that has infiltrated said permeable mass.

This application is a continuation-in-part of Commonly Owned and U.S.patent application Ser. No. 07/854,281, filed Mar. 20, 1992, in thenames of William Bayard Johnson et al. and entitled "Method for FormingCeramic Articles by a Reactive Infiltration Technique and Articles MadeThereby.

TECHNICAL FIELD

This invention relates to a novel method for producing self-supportingcomposite bodies, formed by the oxidation reaction of a parent metal anda solid-phase oxidant to produce at least one oxidation reaction productcomprising, in most cases, at least one intermetallic phase, and,optionally, having at least one metallic component introduced duringformation of the body to impart certain properties to the formed body.The invention also relates to formation of, in some cases, ceramicphases in addition to the intermetallic phase(s).

BACKGROUND ART AND COMMONLY OWNED PATENTS AND PATENT APPLICATIONS

In recent years, there has been an increasing interest in the use ofceramics for structural applications historically served by metals. Theimpetus for this interest has been the superiority of ceramics withrespect to certain properties, such as corrosion resistance, hardness,modulus of elasticity, and refractory capabilities, when compared withmetals.

Current efforts at producing higher strength, more reliable, and tougherceramic articles are largely focused upon (1) the development ofimproved processing methods for monolithic ceramics and (2) thedevelopment of new material compositions, notably ceramic matrixcomposites.

A composite structure is one which comprises a heterogeneous material,body or article made of two or more different materials which areintimately combined in order to attain desired properties of thecomposite. For example, two different materials may be intimatelycombined by embedding one in a matrix of the ether. A ceramic matrixcomposite structure typically comprises a ceramic matrix whichincorporates one or more diverse types of filler materials such asparticulates, fibers, rods, and the like.

There are several known limitations or difficulties in substitutingceramics for metals, such as scaling versatility, capability to producecomplex shapes, satisfying the properties required for the end useapplication, and costs. Several copending patent applications assignedand issued Patents to the same owner as this application (hereinafterreferred to as Commonly Owned Patent Applications and Patents), overcomethese limitations or difficulties and provide novel methods for reliablyproducing ceramic materials, including ceramic composite materials. Themethod is disclosed generically in Commonly Owned U.S. Pat. No.4,713,360, entitled "Novel Ceramic Materials and Methods for MakingSame", which issued on Dec. 15, 1987, from U.S. patent application Ser.No. 06/818,943, filed Jan. 15, 1986, which was a continuation-in-part ofapplication U.S. Ser. No. 06/776,964, filed Sep. 17, 1985, and nowabandoned, which was a continuation-in-part of application Ser. No.06/705,787, filed Feb. 26, 1985, and now abandoned, which was acontinuation-in-part of application Ser. No. 06/591,392, filed Mar. 16,1984, and now abandoned, all in the names of Marc S. Newkirk et al. ThisPatent discloses a method of producing self-supporting ceramic bodiesgrown as the oxidation reaction product of a molten parent precursormetal which is reacted with a vapor-phase oxidant to form an oxidationreaction product. Molten metal migrates through the formed oxidationreaction product to react with the oxidant, thereby continuouslydeveloping a ceramic polycrystalline body which can, if desired, includean interconnected metallic component. The process may be enhanced by theuse of one or more dopants alloyed with the parent metal. For example,in the case of oxidizing aluminum in air, it is desirable to alloymagnesium and silicon with the aluminum to produce alpha-alumina ceramicstructures. This method was improved upon by the application of dopantmaterials to the surface of the precursor metal, as described inCommonly Owned U.S. Pat. No. 4,853,352, entitled "Methods of MakingSelf-Supporting Ceramic Materials and Materials Made Thereby", whichissued on Aug. 1, 1989, from U.S. patent application Ser. No.07/220,935, which was a Rule 62 continuation of commonly owned U.S.patent application Ser. No. 06/822,999, filed Jan. 27, 1986, and nowabandoned which was a continuation-in-part of Ser. No. 06/776,965, filedSep. 17, 1985, and now abandoned, which was a continuation-in-part ofSer. No. 06/747,788, filed Jun. 25, 1985, and now abandoned, which was acontinuation-in-part of U.S. Ser. No. 06/632,636, filed Jul. 20, 1984,and now abandoned, all in the names of Marc S. Newkirk et al.

This oxidation phenomenon was utilized in producing ceramic compositebodies as described in Commonly Owned U.S. Pat. No, 4,851,375, entitled"Methods of Making Composite Ceramic Articles Having Embedded Filler",which issued on Jul. 25, 1989, from U.S. patent application Ser. No.06/819,397, filed Jan. 17, 1986, which was a continuation-in-part ofU.S. Ser. No. 06/697,876, filed Feb. 4, 1985, and now abandoned, all inthe names of Marc S. Newkirk et al. and entitled "Composite CeramicArticles and Methods of Making Same". These patent applications andpatents disclose novel methods for producing a self-supporting ceramiccomposite by growing an oxidation reaction product from a parent metalinto a permeable mass of filler, thereby infiltrating the filler with aceramic matrix. The resulting composite, however, has no defined orpredetermined geometry, shape, or configuration.

A method for producing ceramic composite bodies having a predeterminedgeometry or shape is disclosed in Commonly Owned and Copending U.S. Pat.No. 5,017,526, entitled "Method of Making Shaped Ceramic Composite",which issued on May 21, 1992, from U.S. patent application Ser. No.07/338,741, filed Apr. 14, 1989, as a Rule 62 Continuation of U.S.patent application Ser. No. 06/861,025, filed May 8, 1986, and nowabandoned, in the names of Marc S. Newkirk et al. and entitled "ShapedCeramic Composites and Methods of Making the Same". In accordance withthe method in U.S. Pat. No. 5,017,526, the developing oxidation reactionproduct infiltrates a permeable preform of filler material in thedirection towards a defined surface boundary.

It was discovered that high dimensional fidelity is more readilyachieved by providing the preform with a barrier means, as disclosed inCommonly Owned U.S. Pat. No. 4,923,832, which issued on May 8, 1990,from U.S. patent application Ser. No. 06/861,024, filed May 8, 1986, inthe names of Marc S. Newkirk et al. and entitled "Method of MakingShaped Ceramic Composites with the use of a Barrier". This methodproduces shaped self-supporting ceramic bodies, including shaped ceramiccomposite bodies by growing the oxidation reaction product of aprecursor metal to a barrier means spaced from the metal forestablishing a boundary or surface.

Ceramic composite bodies having a cavity with an interior geometryinversely replicating the shape of a positive parent metal mold orpattern are disclosed in Commonly Owned U.S. Pat. No. 4,828,785,entitled "Inverse Shape Replication Method of Making Ceramic CompositeArticles", which issued on May 9, 1989, from U.S. patent applicationSer. No. 06/823,542, filed Jan. 27, 1986, in the names of Marc S.Newkirk, et al. and entitled "Inverse Shape Replication Method of MakingCeramic Composite Articles and Articles Obtained Thereby", and inCommonly Owned U.S. Patent No. 4,859,640, which issued on Aug. 22, 1989,from U.S. patent application Ser. No. 06/896,157, filed Aug. 13, 1986,in the name of Marc S. Newkirk and entitled "Method of Making CeramicComposite Articles with Shape Replicated Surfaces and Articles ObtainedThereby".

The above-discussed Commonly Owned Patent Applications and Patentsdisclose methods for producing ceramic and/or ceramic composite articleswhich overcome some of the traditional limitations or difficulties inproducing ceramic articles as substitutes for traditional ceramics andmetals in various end-use applications.

Common to each of these Commonly Owned Patent Applications and Patentsis the disclosure of embodiments of a ceramic body comprising anoxidation reaction product interconnected in one or more dimensions(usually in three dimensions) and, if desired, a metallic componentcomprising one or more metallic constituents. The volume of metal, whichtypically includes non-oxidized constituents of the parent metal and/ormetal which has been donated by (e.g., reduced from), for example, anoxidant, a filler or some constituent added to a filler, depends on suchfactors as the temperature at which the oxidation reaction product isformed, the length of time during which the oxidation reaction isallowed to proceed, the composition of the parent metal, the presence ofdopant materials, the presence of reduced constituents from any source,etc. Some of the metallic constituents can be isolated or enclosed, butalso a substantial volume percent of metal can be interconnected andaccessible, or rendered accessible, from an external surface of theceramic body. It has been observed for these ceramic bodies that thismetal-containing component (both isolated and interconnected) can rangefrom about 1 to about 40 percent by volume, and sometimes higher, ifdesired. The metallic component can impart certain favorable propertiesto, or improve the performance of, the ceramic articles in many productapplications. For example, the presence of metal in the ceramicstructure may have a substantial benefit with respect to impartingfracture toughness, thermal conductivity, or electrical conductivity tothe ceramic body.

The entire disclosures of all of the foregoing Commonly Owned PatentApplications and Patents are expressly incorporated herein by reference.

DEFINITIONS

As used herein in the specification and the appended claims, the termsbelow are defined as follow:

"Ceramic" is not to be unduly construed as being limited to a ceramicbody in the classical sense, that is, in the sense that it consistsentirely of non-metallic and inorganic materials, but rather refers to abody which is predominantly ceramic with respect to either compositionor dominant properties, although the body contains minor or substantialamounts of a metallic component comprising one or more metallicconstituents (isolated and/or interconnected), most typically within arange of from about 1-40% by volume, but may include still more metal.

"Oxidation reaction product" means one or more metals in any oxidizedstate wherein the metal(s) has given up electrons to or shared electronswith another element, compound, or combination thereof. Accordingly, an"oxidation reaction product" under this definition includes the productof reaction of one or more constituents of the parent metal with one ormore materials containing one or more solid-phase oxidants, including,for example, the halogens, sulphur and its compounds, oxides, carbides,borides and nitrides. Moreover, the solid-phase oxidant may containmetals such as arsenic selenium, tellurium, molybdenum, niobium, siliconand titanium. Accordingly, this definition includes intermetalliccompounds, alloys, solid solutions or the like formed between anyconstituents of the parent metal and a second or foreign metal which maybe initially present as, for example, at least one component of the oneor more solid-phase oxidants.

"Parent metal" refers to the metal which reacts with the solid-phaseoxidant to form the oxidation reaction product, and includes that metalas a relatively pure metal or a commercially available metal withimpurities; and when a specified metal is mentioned as the parent metal,e.g. aluminum, silicon, titanium, zirconium, hafnium, tin, zinc, etc.,the metal identified should be read with this definition in mind unlessindicate otherwise by the context.

"Second or foreign metal" means any suitable metal, combination ofmetals, alloys, intermetallic compounds, or sources of either, which is,or is desired to be, incorporated as a metallic constituent or phaseinto the metallic component of a formed ceramic body in lieu of, inaddition to, or in combination with unoxidized constituents of theparent metal. This definition includes intermetallic compounds, alloys,solid solutions or the like formed between two or more such second orforeign metals, one or more of which may be initially present as, forexample, at least one component of the one or more solid-phase oxidants.

"Flux" of molten metal means the flow or transport of molten metalwithin the oxidation reaction product, induced by the processconditions. "Flux" as used herein is not meant to define a substance asused in reference to classical metallurgy.

"Parent metal carcass" refers to any remaining parent metal which hasnot been consumed during formation of the self-supporting body, andtypically, which remains in at least partial contact with the formedbody. It should be understood that the carcass may also typicallyinclude some oxidized constituents of the parent metal and/or a secondor foreign metal therein.

SUMMARY OF THE INVENTION

In accordance with a first embodiment of the present invention, there isprovided a method for producing a self-supporting body comprising atleast one intermetallic compound body by the oxidation of a parentmetal, wherein said body comprises the oxidation reaction product of amolten parent metal with a solid-phase oxidant, and a metalliccomponent. Further, a second or foreign metal may be introduced orincorporated into the metallic component of the self-supporting bodyduring the formation of the body in a quantity sufficient to affect, atleast partially, one or more properties of the body.

Generally, in the method for producing a self-supporting body comprisingan intermetallic compound formed by the oxidation of a parent metal, theparent metal is heated to form a body of molten parent metal and isplaced into contact with a solid-phase oxidant. The molten parent metalreacts with the oxidant, at a suitable temperature, to form at least oneintermetallic oxidation reaction product, which product is maintained atleast partially in contact with, and extends between, the body of moltenparent metal and the solid-phase oxidant. At this temperature, moltenparent metal is transported continuously through the intermetallicoxidation reaction product towards the solid-phase oxidant to continuethe reaction. Furthermore, during the process, at least one second orforeign metal also may be incorporated into the flux of molten metal(described below in detail) and thence into the resulting metalliccomponent of the formed body. The resulting metallic component,comprising molten parent metal and at least one second or foreign metal,is transported through the intermetallic oxidation reaction product, andthe parent metal oxidizes as it contacts the solid-phase oxidant,thereby continuously developing a self-supporting body. The oxidationreaction is continued for a time sufficient to form a self-supportingbody comprising an intermetallic oxidation reaction product and ametallic component. The metallic component may comprise nonoxidizedconstituents of the parent metal and at least one second or foreignmetal which may be present in a significant quantity such that one ormore properties of the body are at least partially affected by thepresence and/or properties of the second or foreign metal. By reason ofthe process of this invention, the self-supporting body exhibits one ormore predetermined or desired properties.

In accordance with the present invention, the second or foreign metalmay be introduced into the flux of molten metal during the formation ofthe self-supporting body, and is transported with molten parent metal asa flux of molten metal through the intermetallic oxidation reactionproduct. A portion of the parent metal reacts with the solid-phaseoxidant to form the intermetallic oxidation reaction product while thesecond or foreign metal may remain substantially unoxidized by thesolid-phase oxidant, and typically, is dispersed throughout the metalliccomponent. In one embodiment of the present invention, the second orforeign metal forms as a result of the reaction between the parent metaland the solid-phase oxidant. Specifically, the oxidation of the parentmetal may reduce the solid-phase oxidant to a metallic phase, themetallic phase comprising the second or foreign metal. In a differentembodiment of the present invention, the second or foreign metal isprovided in elemental (e.g., metallic) form. In this particularembodiment, the second or foreign metal may be applied as a layer on thesurface of the parent metal or solid-phase oxidant, or the second orforeign metal may be admixed with the solid-phase oxidant. Regardless ofthe particular embodiment used, upon formation of the self-supportingbody, the second or foreign metal, as a constituent of the metalliccomponent, is an integral part of the formed body, thereby altering orimproving one or more properties of the body.

In another embodiment, wherein a composite is formed and the oxidationreaction product is grown into a mass of filler material or a shapedpreform, the second metal may be provided by admixing the solid-phaseoxidant, homogeneously or non-homogeneously, with the filler material orpreform. As the intermetallic oxidation reaction product forms in theporosity present in the filler material, and the molten metal istransported through the developing intermetallic oxidation reactionproduct, the molten parent metal contacts the second or foreign metal.After such contact, the second metal, or some portion thereof, may beintroduced or incorporated into the flux of molten metal and can betransported into the matrix. The parent metal, or a portion thereof,continues to be oxidized by the solid-phase oxidant at the interfacebetween the solid-phase oxidant and previously formed oxidation reactionproduct, while the second metal may be transported in the flux withinthe formed composite.

In still another embodiment, the second or foreign metal can be providedin the form of an additional compound or mixture (i.e., a compound ormixture having a composition which is different from the solid oxidant)which at least partially reacts with the molten metal, and/ordissociates under process conditions, to liberate the second metal whichcan then be introduced or incorporated into the flux of molten metal.Such additional compound or mixture may be applied, for example, as alayer on top of the parent metal body, or admixed with or applied to afiller material or preform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic view of the setup used in carryingout the composite fabrication process of Example 1;

FIGS. 2A and 2B are optical photomicrographs taken at about 53× andabout 425× magnifications, respectively, of a polished cross-section ofthe formed composite material of Example 1;

FIG. 3 is an optical photomicrograph taken at about 53× magnification ofa polished cross-section of the formed composite material of Example 2;

FIG. 4 is a cross-sectional schematic view of the setup used in carryingout the composite fabrication process of Example 3;

FIG. 5 is an optical photomicrograph taken at about magnification of apolished cross-section of the Sample A composite material of Example 3;

FIGS. 6A and 6B are optical photomicrographs taken at about 53× andabout 425× magnifications, respectively, of a polished cross-section ofthe Sample B composite material of Example 3;

FIGS. 7A and 7B are optical photomicrographs taken at about 53× andabout 425× magnifications, respectively, of a polished cross-section ofthe Sample C composite material;

FIGS. 8A and 8B are optical photomicrographs taken at about 53× andabout 380× magnifications, respectively, of a polished cross-section ofthe Sample D composite material;

FIGS. 9A and 9B are optical photomicrographs taken at about 53× andabout 425× magnifications, respectively, of a polished cross-section ofthe Sample E composite material;

FIG. 10A is a scanning electron photomicrograph taken usingbackscattered electron imaging at about 50× magnification of a polishedcross-section of the Sample F composite material;

FIG. 10B is an optical photomicrograph taken at about 106× magnificationof a polished cross-section of the Sample F composite material;

FIG. 11 is an optical photomicrograph taken at about 106× magnificationof a polished cross-section of the Sample G composite material;

FIG. 12 is an optical photomicrograph taken at about 106× magnificationof a polished cross-section of the Sample H composite material;

FIGS. 13A and 13B are optical photomicrographs taken at about 53× and425× magnification, respectively, of a polished cross-section of theSample I composite material;

FIG. 14 is an optical photomicrograph taken at about 106× magnificationof a polished cross-section of the Sample J composite material.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In accordance with the present invention, the parent metal, which maycontain a dopant (as explained below in greater detail), is formed intoan ingot, billet, rod, plate, or the like; and is placed into anappropriate setup, comprising, for example, an inert bed, crucible orother refractory container. It has been discovered that a second orforeign metal can be combined with molten parent metal during formationof the self-supporting body, either containing or not containing afiller, to form a flux of metal. The resulting parent metal and secondmetal flux may be transported through the previously formed oxidationreaction product by, for example, capillary transport of the flux ofmolten metal, in a manner similar to that manner described in theCommonly Owned Patents and Patent Applications. Thus, the second orforeign metal may become an integral part of the metallic component ofthe formed body.

A predetermined quantity of a solid-phase oxidant can be provided to thesetup comprising the parent metal, said inert bed, crucible or otherrefractory container, and optionally a composite filler material orpreform. Specifically, by placing the solid-phase oxidant into contactwith one or more surfaces of the parent metal or, in cases where acomposite is formed, by admixing the solid-phase oxidant with the fillermaterial or preform and heating the parent metal to form molten parentmetal, reaction between the parent metal and the solid-phase oxidant canoccur (which techniques are discussed in greater detail below). The bodyis then recovered, said body having a metallic component comprisingunoxidized constituents of the parent and, if desired, the second metal.Moreover, the metallic component of the formed body comprisesinterconnected and/or isolated metallic inclusions.

In the practice of the present invention, the choice of the solid-phaseoxidant(s) and parent metal(s) are based primarily upon one or moreproperties desired for the body to be formed. The metallic component canimpart certain favorable properties to, or improve the performance of,the formed body With respect to its intended use. For example, ametallic component in the body can beneficially improve the fracturetoughness, thermal conductivity, environmental compatibility, andelectrical conductivity of the body, depending upon such factors as thecomposition of the metallic component and the amount and distribution ofthe metallic component throughout the formed body. By providing a methodfor tailoring the constituents of the metallic component to includemetals or metallic phases in addition to or other than the parent metal,the invention adds substantial latitude to the end-use applications forsuch formed bodies. In order to impart the desired property(ies) to theformed body, second or additional metals should be chosen which do notform an oxidation reaction product preferentially to the parent metalunder the particular process conditions utilized. Typically, a secondmetal satisfies that criterion if its oxidation reaction product has aless negative free energy of formation at a given reaction temperaturethan that of the parent metal, with respect to the particular oxidationreaction occurring with the solid-phase oxidant present.

The second or foreign metal may alloy or react with the parent metalwithin the metallic component when such second or foreign metal has achemical composition which is different from the composition of theparent metal. Additionally, the second or foreign metal may react withone or more components of the solid-phase oxidant to form, for example,alloys or additional intermetallic compounds, which may be desirable, orimpart desirable attributes to the resulting body. Thus, in accordancewith the present invention, there is also provided a method for the insitu formation of one or more desired metallic phases comprising one ormore of the metallic constituents of the parent metal, one or moresecond or additional metals and one or more components of thesolid-phase oxidant (e.g., a product or products of the reaction withthe solid-phase oxidant). Such metallic phases include intermetalliccompounds, solid solutions, alloys or combinations of each. In thepresent embodiment, a suitable solid-phase oxidant is chosen such thatthe resultant body includes at least one at least one desirableoxidation reaction product and desirable metallic phase. For example, asolid-phase oxidant may be chosen such that a second metal forms one ormore metallic phases in combination with the parent metal, at a giventemperature aria relative concentration, which are desirable to beincorporated into, for example, the metallic component of the formedbody. The second or additional metal may be provided and introduced intothe flux of molten metal in a lower relative concentration than isneeded to form the desired metallic phase or phases in the resultantbody. As the molten parent metal reacts with the solid-phase oxidant ata given reaction temperature, thus forming at least one oxidationreaction product, the relative concentration of parent metal within theinterconnected metallic component (i.e., flux) is depleted or reduced.Therefore, the relative concentration of the second metal increaseswithin the metallic component of the formed body. The reaction iscontinued at a given reaction temperature or within a temperature rangeuntil a sufficient quantity of parent metal has been depleted from themolten metal flux leading to the formation of one or more desiredmetallic phase(s), comprising, in some cases, the parent metal andsecond metal. Alternatively, the oxidation reaction can be continued fora time sufficient to deplete an amount of parent metal such that, uponreducing the reaction temperature, or cooling the formed body, thedesired metallic component formation occurs, thus forming or enrichingthe desired metallic phase comprising, in some cases, the parent metaland second metal. The resulting metallic phase or phases can eitherinherently impart a desirable property or properties to the body, or canbe of such a composition that will form one or more additional phases ata given service temperature, thereby imparting the desired property orproperties to the formed body. Additionally, by the manipulation ofreaction parameters (e.g. reaction time, reaction temperature, etc.) orby the appropriate combination or addition of certain metals, themetallic component of a formed body can be further tailored as in, forexample, precipitation hardening of a desired alloy within the metalliccomponent.

Since the method herein disclosed of optionally incorporating a secondor foreign metal into the metallic component of a formed body involvesthe intimate combination of two or more metals, viz. the second metaland parent metal, it should be understood that the latitude affordedwith respect to the identity, quantity, form, and/or concentration ofsecond metal relative to the parent metal to be employed will dependupon the metallic constituents or phases which are desired to beincorporated into the body, and the process conditions necessary for theformation of the desired oxidation reaction product(s). The inclusionand/or formation of the desired metallic constituents will be governed,at least in part, by the properties and/or physical metallurgyassociated with the combination or interaction of the particular metalspresent under the particular process conditions, and/or the solid-phaseoxidant chosen for reaction with the parent metal. This combination ofmetals may effect the formation of various metallic phases, includingalloys, intermetallic compounds, solid solutions (including relativelypure elements), precipitates, or mixtures thereof, and may be affectedby the presence and concentration of impurities and/or dopant materials.Thus, the metallic component resulting from combination of the metals inthe practice of the present invention can have properties which varysignificantly from those of the several metals individually. Suchcombinations comprising the parent metal and second metal incorporatedinto the metallic component of the formed ceramic body canadvantageously affect properties of the formed body. For example, thecombination of second metal and parent metal may form one or moremetallic phases such as solid solutions, alloys or one or moreadditional intermetallic compounds which have a melting point above thatof the parent metal, thereby expanding the service temperature range ofa ceramic body having such (a) metallic phase(s) incorporated therein as(a) metallic constituent(s) of the metallic component of the body.Moreover, it should be understood that in some cases the melting pointof the resulting metallic constituent(s) may be above the operabletemperature range for the formation of the intended oxidation reactionproduct. Additionally, the formation of metallic constituents resultingfrom certain combinations of parent and second metals may impart addedviscosity to the resulting molten metal at the reaction temperature, ascompared with molten parent metal without the addition of second metalat the same temperature, such that the transport of molten metal throughthe formed oxidation reaction product substantially slows or does notoccur. As such, care should be taken with respect to designing a desiredsystem which includes such a combination of parent and second metals inorder to ensure that the metallic component remains sufficiently liquidwhile the oxidation reaction product is being formed to facilitate thecontinued flux of molten metal at a temperature which is compatible withthe parameters of the oxidation reaction process.

Additional factors to be considered when selecting an appropriatesolid-phase oxidant material include the metallurgical propertiesassociated with the contact of the molten parent metal with the secondmetal in order to effect introduction of the desired quantity of secondmetal into the flux of the metallic component. For example, when asolid-phase oxidant is reduced by the parent metal to liberate a secondmetal into the metallic component, interdiffusion of the two metals, orreaction of the two metals as in the formation of one or more additionalintermetallic compounds, ceramic compounds or other metallic phasesbetween the parent metal and second metal may occur. Thus, theintroduction and/or rate of introduction of second metal into the fluxof the metallic component will depend on one or more of several suchmetallurgical factors. Such factors include the physical state of thesecond metal at the particular reaction temperature, the rate ofinterdiffusion between the parent metal and second metal, the degreeand/or rate of solubility of the second metal into the parent metal orthe parent metal into the second metal, and the formation of additionalintermetallics or other metallic phases between the parent metal andsecond metal. Thus, care should be taken to ensure that the reactiontemperature is maintained such that the metallic constituents, resultingfrom the introduction of second metal into the flux of the metalliccomponent of the formed body, remain at least partially liquid tofacilitate the transport of the metallic constituents through themetallic component into the formed oxidation reaction product, and thusenable contact of the molten parent metal with the solid-phase oxidantin order to facilitate formation of the body. In accordance with thepresent invention, the introduction of a second metal into the flux ofmolten metal, or the depletion of parent metal from the flux of moltenmetal due to formation of the oxidation reaction product, can result inthe formation of one or more metallic phases comprising the parent metaland second metal. However, metallic phases comprising certaincombinations of parent metal and second metal may impart significantviscosity to the metallic component of the forming body, or otherwiseimpede the flux of the molten metal fraction of the metallic componentsuch that transport of metal toward the solid-phase oxidant ceases priorto the complete development of the desired oxidation reaction product.In such cases, the formation of the desired oxidation reaction productmay be halted or substantially slowed by those phenomena and, therefore,care should be exercised to avoid the premature or excessive formationof such metallic phases.

Numerous types of reactions and the composite materials produced therebyshould be readily apparent to those of ordinary skill in the art. Someof these examples, under the appropriate reaction conditions, mayinclude those material combinations set forth in Table I. However,

                  TABLE I                                                         ______________________________________                                        Possible Reaction Combinations                                                                                      Oxidation                                                           Second or Reaction                                Parent   Solid-Phase        Foreign   Product                                 Metal    Oxidant    Atm.    Metal     Matrix                                  ______________________________________                                        1.  Ti       Si.sub.3 N.sub.4                                                                         Ar    Ti.sub.5 Si.sub.3                                                                       TiN                                   2.  Al       NbO.sub.2  Ar    NbAl.sub.3                                                                              Al.sub.2 O.sub.3                      3.  Ti       SiB.sub.6  Ar    MoSi.sub.2                                                                              TiB.sub.2                             4.  Nb/Al    NbO.sub.2  Ar    NbAl.sub.3 /NbAl.sub.2                                                                  Al.sub.2 O.sub.3                      ______________________________________                                    

specific working examples of the invention are set forth in the Exampleslater herein.

In certain embodiments of the invention, where the product is acomposite fabricated by growing the oxidation reaction product into amass or aggregate of filler material or a permeable preform, whichfiller material or preform may be placed adjacent to the parent metal,the solid-oxidant material may be provided by admixing it with thefiller material or preform material, or applied, as in layering, to oneor more surfaces of the filler material or preform. The solid-phaseoxidant may also be applied on only one or more surfaces of a mass oraggregate of filler material or shaped preform. Application of asolid-phase oxidant to one or more surfaces of a mass of filler materialor preform in accordance with the present embodiment can result in acomposite body wherein the exposed portions of the metallic componentare rich in the second or foreign metal from the solid-phase oxidantrelative to other portions of the metallic component within the formedcomposite body.

The solid-phase oxidant can be provided in the form of a mixture orcompound which will react with the molten parent metal, and/ordissociate under the process conditions, to liberate the second orforeign metal therefrom, which is then introduced, as discussed above,into the flux of molten metal. Such a compound may be a metal oxide,nitride, carbide, boride, etc., which is reducible by, or will reactwith, the parent metal to liberate the second metal(s). For example, ifa composite body is desired comprising a ceramic matrix, fabricated bythe oxidation of an aluminum parent metal, to embed particles of analumina filler material, a solid-phase oxidant (e.g., a single, binary,ternary or higher order oxide, nitride, carbide, boride, etc.)containing desired second metal(s) such as silicon, nickel, iron, orchromium may be admixed with the alumina filler material, or layered ontop of the aluminum parent metal. For example, if chromium is desired asa second metal, chromium metal can be introduced into the flux of moltenmetal by admixing chromium oxide with a filler material. When the fluxof the molten aluminum contacts the chromium oxide, some of the moltenaluminum will reduce the chromium oxide and liberate chromium metal. Aquantity of the liberated chromium metal is then introduced into theflux of the remaining molten aluminum, as discussed above, andtransported through and/or into the oxidation reaction product which isformed as the molten aluminum parent metal continues to contact thechromium oxide solid-phase oxidant.

As explained in the Commonly Owned Patents and Patent Applications,dopant materials, used in conjunction with the metal, favorablyinfluence the oxidation reaction process. Additionally, in the practiceof the present invention, in certain cases a dopant material may bechosen to, in addition to its doping qualities, provide a second orforeign metal or a source of the same which is desirable to beincorporated into the metallic component of the formed body. However, insome cases, a suitable dopant material will not be available whichsupplies the necessary doping characteristics and a source of thedesired second or foreign metal and/or solid-phase oxidant. Therefore, adopant material may need to be used in conjunction with the second orforeign metal and/or solid-phase oxidant. It should be noted, however,that when employing a dopant material in conjunction with a solid-phaseoxidant, the presence of each may have an effect upon the functionand/or performance of the other. Thus, in practicing certain embodimentsof the present invention, where it is desirable to effect the formationof one or more metallic constituents comprising the parent metal andsecond metal, and, additionally, where a separate dopant material isemployed, the respective concentrations of parent metal and solid-phaseoxidant necessary to effect formation of the desired constituent(s) maybe different than the concentrations necessary to effect formation ofthe metallic constituents in the binary system comprising the parentmetal and solid-phase oxidant. Therefore, care should be taken toconsider the effect of all materials present in a specific case whendesigning a system wherein it is desired to effect the formation of oneor more metallic constituents within the metallic component of theformed body. The dopant or dopants used in conjunction with the parentmetal, as in the case of second metals, (1) may be provided as alloyingconstituents of the parent metal, (2) may be applied to at least aportion of the surface of the parent metal, or (3) may be applied to orincorporated into part or all of the filler material or preform, or anycombination of two or more of techniques (1), (2), or (3) may beemployed. For example, an alloyed dopant may be used alone or incombination with a second externally applied dopant. In the case oftechnique (3), wherein additional dopant or dopants are applied to thefiller material, the application may be accomplished in any suitablemanner as explained in the Commonly Owned Patents and PatentApplications.

The function or functions of a particular dopant material can dependupon a number of factors. Such factors include, for example, theparticular combination of dopants when two or more dopants are used, theuse of an externally applied dopant in combination with a dopant alloyedwith the parent metal, the concentration of dopant employed, theoxidizing environment, process conditions, and as stated above, theidentity and concentration of the second metal present.

As disclosed in the above-discussed U.S. Pat. No. 4,923,832, a barriermeans may be used to inhibit growth or development of the oxidationreaction product beyond the barrier. Suitable barrier means may be anymaterial, compound, element, composition, or the like, which, under theprocess conditions of this invention, maintains some integrity, is notvolatile, and is capable of locally inhibiting, poisoning, stopping,interfering with, preventing, or the like, continued growth of oxidationreaction product. Suitable barriers include calcium sulfate (Plaster ofParis), calcium silicate, and Portland cement, and combinations thereof,which typically are applied as a slurry or paste to the surface of thefiller material. Still further, the barrier means may include a suitablerefractory particulate to reduce any possible shrinkage or crackingwhich otherwise may occur during the process. Such a particulate havingsubstantially the same coefficient of expansion as that of the fillermaterial is especially desirable.

This invention is further illustrated in the following non-limitingExample.

EXAMPLE 1

This Example demonstrates the fabrication of a composite body comprisinga niobium aluminide (NbAl₃) intermetallic. FIG. 1 is a cross-sectionalschematic view of the setup used in carrying out the compositefabrication process. This Example should not be construed as beinglimited to the above-described embodiment, however, but instead as alsodisclosing other important aspects of the claimed invention.

About 6.94 grams of titanium diboride particulate having substantiallyall particles smaller than about 45 μm in diameter (-325 mesh,Consolidated Astronautics Co., Saddle Brook, N.J.) and about 13.1 gramsof niobium particulate having substantially all particles smaller thanabout 45 microns in diameter (-325 mesh, Consolidated Astronautics Co.)were hand mixed in a weighing dish. The particulate mixture was thenpoured into a Grade ATJ graphite crucible 10 (Union Carbide Corp.,Carbon Products Division, Cleveland, Ohio) measuring about 1.5 inches(37 mm) in interior diameter by about 2.5 inches (64 mm) high and handtapped to collapse any excessive porosity between the particles, therebyforming a permeable mass 12. About 0.34 grams of magnesium particulate16 having substantially all particles between about 300 and about 700microns in diameter (-24+50 mesh, Hart Corp., Tamaqua, Pa.) wassprinkled evenly over the leveled permeable mass 12 of niobium andtitanium diboride. A parent metal ingot 14 weighing about 25.4 grams andcomprising commercially pure aluminum was then placed on top of thelayer of magnesium particulate 16 to form a lay-up 18. The graphitecrucible 10 and its contents were then placed into a graphitecontainment boat 20 measuring about 5 inches (127 mm) square by about 2inches (51 mm) in height and covered with a GRAFOIL® graphite foil sheet22.(Union Carbide Co., Carbon Products Div., Cleveland, Ohio) tocomplete the experimental setup 24.

The setup 24 comprising the graphite containment boat 20 and itscontents was then placed into the vacuum chamber of a vacuum furnace atabout 25° C. The chamber was then sealed, and twice evacuated to lessthan about 4×10-4 torr and backfilled to substantially atmosphericpressure with commercially pure argon gas. An argon gas flow rate ofabout 4000sccm was thereafter established and maintained at a pressureabove atmospheric pressure of about 5 psi (35,000 Pa). The temperatureinside the furnace chamber was then increased from about 25° C. to atemperature of about 1000° C. at a rate of about 200° C. per hour. Aftermaintaining a temperature of about 1000° C. for about 10 hours, thetemperature in the chamber was then decreased back to about 25° C. at arate of about 200° C. per hour.

When the temperature in the vacuum chamber had cooled to substantiallyambient temperature (e.g., about 25° C.), the pressure in the chamberwas equilibrated with the ambient atmospheric pressure, the chamber wasopened and the setup 24 was recovered and disassembled to reveal that acomposite body had formed.

A portion of the formed composite material was analyzed qualitatively byx-ray diffraction. This sample was prepared by chipping off some of theformed composite material and grinding it to a fine powder in a mortarand pestle. The powdered sample was placed into the sample chamber of anx-ray diffractometer (Model D500, Siemens AG, Munich, Germany) andscanned with unfiltered Cu_(K)α x-radiation at an energy of about 40KeV. The counting time was about two seconds at each 0.030 degreeinterval of two-theta. This x-ray diffraction analysis revealed thepresence of NbAl₃, Al and TiB₂.

Another portion of the composite body was sectioned with a diamond saw,mounted in plastic and polished with progressively finer grades ofdiamond polishing compound in preparation for microscopic examination.FIGS. 2A and 2B are optical photomicrographs taken at about 53× and 425×magnification, respectively, of such a polished cross-section.

Thus, this Example demonstrates that a composite body comprising aniobium aluminide intermetallic oxidation reaction product can be formedby reactively infiltrating a parent metal comprising aluminum into apermeable mass comprising niobium.

EXAMPLE 2

This Example demonstrates the fabrication of a composite body comprisingan oxidation reaction product comprising a titanium aluminideintermetallic. The setup used to fabricate this composite material wassubstantially the same as than shown in FIG. 1. This Example should notbe construed as being limited to the above-described embodiment,however, but instead as also disclosing other important aspects of theclaimed invention.

About 20 grams of titanium particulate having substantially allparticles smaller than about 45 μm in diameter -325 mesh, ConsolidatedAstronautics Co., Saddle Brook, N.J. and about 20.1 grams of titaniumdiboride having substantially all particles between about 1 and 5 μm indiameter Atlantic Equipment Engineers, Bergenfield, N.J.) were handmixed together in a weighing dish to a uniform color. The particulateadmixture was then poured into a Grade ATJ graphite crucible 10 (UnionCarbide Co., Carbon Products Division, Cleveland, Ohio) having an insidediameter of about 1 inch (25 mm) and a height of about 2.5 inches 64 mm)and leveled. The graphite crucible 10 and its contents were then handtapped to collapse any excessive void space between the particles,thereby forming the particulate admixture into a permeable mass 12.About 0.2 grams of magnesium particulate 16 having substantially allparticles between about 300 and 700 μm in diameter (-24+50 mesh, HartCorp. Tamaqua, Pa.) was then sprinkled on Tamaqua, Pa.) was thensprinkled on top of the particulate admixture in the graphite crucible10. An ingot of parent metal 14 weighing about 35.5 grams and comprisingcommercially pure aluminum was then placed into the graphite crucible 10on top of the magnesium particulate layer 16 to form a lay-up 18. Thegraphite crucible 10 and its contents was then placed into a graphitecontainment boat 20 measuring about 3 inches (76 mm) square by about3.25 inches (83 mm) in height. The opening at the top of the boat wascovered with a GRAFOIL® graphite foil sheet 22 in substantially the samemanner as was described in Example 1 to form a setup 24.

The setup 24 comprising the graphite containment boat 20 and itscontents was then placed into the vacuum chamber of a vacuum furnace.The chamber was sealed, and then twice evacuated and backfilled withargon gas in substantially the same manner as was described in Example 1. A commercially pure argon gas flow rate of about 4000 to 5000 sccm wasthen established and maintained through the vacuum chamber at a pressureabove atmospheric pressure of about 5 psi (35,000 Pa). The temperatureinside the vacuum chamber was then increased from a temperature of about25° C. to a temperature of about 800° C. at a rate of about 200° C. perhour. After maintaining a temperature of about 800° C. for about 10hours, the furnace chamber and its contents were then cooled to about25° C. at a rate of about 200° C. per hour.

After the temperature inside the vacuum chamber had cooled to about 25°C., the pressure in the vacuum chamber was equilibrated with the ambientatmospheric pressure, the chamber was opened and the setup 24 comprisingthe graphite containment boat 20 and its contents was recovered anddisassembled in substantially the same manner as in Example 1 to revealthat a composite body had formed. This composite body was recovered fromthe lay-up 18.

The composite body was sectioned with a diamond saw, mounted in plasticand polished with progressively finer grades of diamond polishingcompound in preparation for microscopic examination. FIG. 3 is anoptical photomicrograph taken at about 53× magnification of thispolished cross-section.

Subsequent qualitative x-ray diffraction analysis of the composite bodyperformed in substantially the same manner as described in Example 1revealed the presence of TiAl₃, TiB₂ and possibly a trace of TiO₂ asanatase.

Thus, this Example demonstrates that a composite body comprising TiAl₃titanium aluminide intermetallic oxidation reaction product can beproduced by the reactive infiltration of a parent metal comprisingaluminum with a permeable mass comprising titanium.

EXAMPLE 3

This Example demonstrates the fabrication of composite bodies comprisingtitanium aluminide intermetallics by the reactive infiltration of aparent metal comprising titanium. The setup employed in fabricatingthese composite bodies is shown schematically in FIG. 4. This Exampleshould not be construed as being limited to the above-describedembodiment, however, but instead as also disclosing other importantaspects of the claimed invention.

SAMPLE A

This experiment specifically demonstrates the reactive infiltration of aparent metal comprising titanium into a permeable mass comprisingtitanium and aluminum nitride to form a composite body comprising atitanium aluminide intermetallic.

About 5.8 grams of titanium particulate having substantially allparticles smaller than about 45 μm in diameter -325 mesh, ConsolidatedAstronautics Co., Saddle Brook, N.J. and about 4.2 grams of Grade A-200aluminum nitride particulate (Advanced Refractory Technologies, Inc.,Buffalo, N.Y.) were mixed by hand in a weighing dish until a uniform huewas achieved. The particulate mixture was then loaded into a Grade ATJgraphite crucible 10 (Union Carbide Company, Carbon Products Division,Cleveland, Ohio) having an inside diameter of about 1.25 inches (32 mm)and a height of about 2.5 inches (64 mm). The graphite crucible 10 andits contents were then hand tapped several times to collapse anyexcessive void space between the particles, thereby forming theparticulate mixture into a permeable mass 12. A parent metal 14comprising titanium sponge having substantially all granule sizesbetween about 850 and 4000 μm (-5 +20 mesh, Micron Metals, Inc., SaltLake City, Utah) was poured into the graphite crucible 10 on top of thepermeable mass 12 to form the Sample A lay-up 18.

SAMPLE B

This experiment specifically demonstrates the reactive infiltration of aparent metal comprising titanium into a permeable mass comprisingtitanium diboride and aluminum nitride to form a composite bodycomprising a titanium aluminide intermetallic.

About 8.5 grams of Grade A-200 aluminum nitride particulate (AdvancedRefractory Technologies, Inc.) and about 11.6 grams of titanium diborideparticulate (1-5 micron average particle diameter, Atlantic EquipmentEngineers, Bergenfield, N.J.) were hand mixed in a weighing dish until auniform hue was achieved. The particulate admixture was then poured intoa Grade ATJ graphite crucible 10 having an inside diameter of about 1.5inches (37 mm) and a height of about 2.5 inches (64 mm). The particulateadmixture was leveled and the crucible was tapped by hand several timesto collapse any excessive void space between the particles, therebyforming the particulate admixture into a permeable mass 12. About 39.2grams of a parent metal 14 comprising titanium sponge havingsubstantially all granule sizes between about 300 and about 700 micronsin diameter (Micron Metals, Inc.) was then poured into the graphitecrucible 10 and spread evenly over the surface of the permeable mass 12to complete the Sample B lay-up 18.

The lay-ups 18 for Samples A and B were then placed into a graphitecontainment boat 20 measuring about 10 inches (254 mm) square by about 4inches (102 mm) in height. The opening at the top of the boat wascovered with a GRAFOIL® graphite foil sheet 22 (Union Carbide Co.) tocomplete the setup 24. The setup 24 comprising the graphite containmentboat 20 and its contents was then placed into the vacuum chamber of avacuum furnace at a temperature of about 25° C. The chamber was sealed,and then twice evacuated to about 2×10⁻⁴ torr and backfilled withcommercially pure argon gas to about atmospheric pressure. An argon gasflow rate through the vacuum chamber of about 2000 sccm at a pressureabove atmospheric pressure of about 5 psi (35,000 Pa) was thereafterestablished and maintained. The temperature in the vacuum chamber wasthen increased from about 25° C. to a temperature of about 1700° C. at arate of about 300° C. per hour. After maintaining a temperature of about1700° C. for about 10 hours, the temperature was then decreased back toabout 25° C. at a rate of about 200° C. per hour. After the temperaturein the vacuum chamber had decreased to about 25° C., the pressure in thechamber was equilibrated with ambient atmospheric pressure, the chamberwas opened and the setup 24 comprising the graphite containment boat 20and its contents was removed from the vacuum chamber and disassembled.For each of Samples A and B, a composite body had been formed as thepermeable mass of particulate matter in each graphite crucible appearedto have been completely infiltrated.

Each composite body was sectioned with a diamond saw, mounted in plasticand polished with progressively finer grades of diamond polishingcompound in preparation for microscopic examination. Furthermore, eachcomposite body was analyzed qualitatively using x-ray diffractionsubstantially as described in Example 1.

FIG. 5 is an approximately 53× magnification optical photomicrograph ofa polished cross-section of the Sample A composite material. FIGS. 6Aand 6B are approximately 53× and 425× magnification, respectively,optical photomicrographs of a polished cross-section of the Sample Bcomposite material.

The x-ray diffraction analysis of the Sample A composite materialrevealed the presence of TiC, TiN and Ti₉ Al₂₃ phases. The x-raydiffraction analysis of the Sample B composite material revealed thepresence of TiC, TiN, TiB₂, TiAl₃ phases and possibly some residual Al.

Thus, this Example demonstrates that a composite body comprising Ti₉Al₂₃ or TiAl₃ titanium aluminide intermetallics may be formed by thereactive infiltration of a molten parent metal comprising titanium intoa permeable mass comprising aluminum nitride.

EXAMPLE 4

This Example demonstrates the fabrication of composite bodies comprisingMoSi₂ molybdenum disilicide intermetallic. The setup employed wassubstantially the same as that shown in FIG. 1. This Example should notbe construed as being limited to the above-described embodiment,however, but instead as also disclosing other important aspects of theclaimed invention.

SAMPLE C-E

A lay-up for fabricating a composite body by the methods of the presentExample was prepared as follows:

Molybdenum dioxide and alumina particulates were roll mixed for about 1hour in the absence of milling or grinding media. The roll mixedparticulate admixture was then placed into an approximately 2 inch (51mm) square box constructed from GRAFOIL® graphite foil sheet material(Union Carbide Co., Carbon Products Division, Cleveland, Ohio) andleveled. The GRAFOIL® graphite foil box and its contents were than handtapped several times to consolidate the particulates contained withinand thereby collapsing any excessive void space between the particles.The graphite foil box was constructed from a single sheet of GRAFOIL®graphite foil material measuring about 0.015 inches (0.4 mm) thick bymaking strategically placed cuts and folds in the sheet material andstapling the seams to form a five-sided box. An ingot of a parent metalcomprising by weight about 30% silicon, 5% magnesium and the balancealuminum was then placed into the graphite foil box on top of theparticulate admixture. At the interface between the ingot of parentmetal and the admixture of molybdenum dioxide and alumina particulateswas sprinkled a uniform layer of initiator material comprising magnesiumparticulate wherein substantially all of the magnesium particles werebetween about 300 μm and 700 μm in diameter (-24, +50 mesh, HartCorporation, Tamaqua, Pa.).

Table 1 reports the specific quantities of the above-mentioned materialsemployed in fabricating the lay-up for each of Samples C-E.

                  TABLE 1                                                         ______________________________________                                                                        Parent                                        Sam-                   Initiator                                                                              Metal Preform                                 ple  Permeable Mass    wt (g)   wt (g)                                                                              wt (g)                                  ______________________________________                                        C     100 g MoO.sub.2.sup.a,  100 g Al.sub.2 O.sub.3.sup.b                                           0.41     151   76                                      D      25 g MoO.sub.2.sup.a,   75 g Al.sub.2 O.sub.3.sup.b                                           0.78     204   84                                      E    10.1 g MoO.sub.2.sup.a, 90.1 g Al.sub.2 O.sub.3.sup.b                                           0.88     201   86                                      ______________________________________                                         .sup.a Alfa Products, Div. of Johnson Matthey Co., Ward Hill, MA, 99% pur     .sup.b EGPA alumina, 15 μm average particle size, Norton Co.,              Worcester, MA                                                            

The lay-ups of Samples C, D and E were then placed into a graphitecontainment boat 20 measuring about 10 inches (254 mm) square by about 4inches (102 mm) in height. The opening at the top of the boat 20 wascovered with a GRAFOIL® graphite foil sheet 22 (Union Carbide Co.) tocomplete the setup 24.

The setup 24 comprising the graphite containment boat 20 and itscontents was then placed into the vacuum chamber of a vacuum furnace ata temperature of about 150° C. The vacuum chamber was sealed and thecontents of the vacuum chamber were twice evacuated to less than about30 inches (760 mm) of mercury vacuum and backfilled with commerciallypure nitrogen gas to about atmospheric pressure. After the secondbackfill, a nitrogen gas flow rate of about 4000 sccm was establishedand maintained in the vacuum chamber at a pressure above atmosphericpressure of about 5 psi (35,000 Pa).

The temperature of the vacuum chamber and its contents was thenincreased from about 150° C. to a temperature of about 925° C. at a rateof about 200° C. per hour. After maintaining a temperature of about 925°C. for about 10 hours, the temperature of the vacuum chamber and itscontents was then decreased to a temperature of about 825° C. at a rateof about 400° C. per hour. At a temperature of about 825° C., thepressure of the vacuum chamber was brought back to about ambientatmospheric pressure, the vacuum chamber was opened and the setupcomprising the graphite containment boat and its contents was removedfrom the vacuum chamber and allowed to cool naturally in air back to atemperature of about 20° C.

Once the setup had cooled substantially to about 20° C., the variouslay-ups contained in the setup were disassembled. Specifically,disassembly of the Samples C and D lay-ups revealed that the permeablemass comprising the particulate admixture of molybdenum dioxide andaluminum oxide had been infiltrated to a depth of a few millimeters.Disassembly of the Sample E lay-up revealed that the permeable masscomprising this particulate admixture had been completely infiltrated.Each composite body was x-ray diffraction analyzed substantially inaccordance with the procedure of Example 1. Furthermore, each compositebody was sectioned with a diamond saw, mounted in plastic and polishedwith progressively finer grades of diamond polishing compound inpreparation for microscopic examination.

The x-ray diffraction analysis of the formed Sample C composite materialrevealed the presence of the following phases in the formed compositematerial: Al, Si, MoSi₂, α-Al₂ O₃, MgAl₂ O₄ and Mo. FIGS. 7A and 7B areoptical photomicrographs taken at about 53× and about 425×magnifications, respectively, of polished cross-section of the Sample Ccomposite material.

The x-ray diffraction analysis of the formed Sample D composite materialrevealed the presence of the following phases: Al, Si, MoSi₂ and α-Al₂O₃. FIGS. 8A and 8B are optical photomicrographs taken at about 53× andabout 380× magnifications, respectively, of a polished cross-section ofthe Sample D composite material.

The x-ray diffraction analysis of the formed Sample E composite materialrevealed the presence of the following phases in the formed compositematerial: Al, Si, MoSi₂, α-Al₂ O₃ and AlN. FIGS. 9A and 9B are opticalphotomicrographs taken at about 53× and about 425× magnifications,respectively, of a polished cross-section of the Sample E compositematerial.

Thus, this Example demonstrates that a composite body comprising anoxidation reaction product comprising MoSi₂ molybdenum disilicideintermetallic can be formed by reactively infiltrating a parent metalcomprising silicon into a permeable mass comprising molybdenum dioxideand alumina.

EXAMPLE 5

This Example demonstrates the fabrication of a composite body comprisingan oxidation reaction product comprising MoSi₂ molybdenum disilicideintermetallic. The setup employed in fabricating the composite bodies ofthis Example was substantially the same as that shown in FIG. 4. ThisExample should not be construed as being limited to the above-describedembodiment, however, but instead as also disclosing other importantaspects of the claimed invention.

SAMPLES F-J

The lay-ups for Samples F-J were fabricated in substantially the samemanner with the exception that the parent metal for Samples I and Jcomprised a hand-mixed admixture of ALFA® silicon (Alfa Products,Division of Johnson-Matthey Co., Ward Hill, Mass., 99.999pure) andAESAR® aluminum (Aesar Group of Johnson-Matthey Co., Seabrook, N.H.,99.9% pure) granules.

Table 2 contains a list of the particular amounts of the various rawmaterials used in assembling each lay-up.

                  Table 2                                                         ______________________________________                                        Sample                                                                              Wt. Mo.sup.1                                                                           Wt. SiC.sup.2                                                                          Parent Metal                                                                            Wt. Parent Metal                            ______________________________________                                        F     26.5 g   26.5 g   Si.sup.3, 5n pure                                                                           100.7 g                                 G     15       45.0     Si, 5n pure                                                                             100.4                                       H      5.1     45.6     Si, 5n pure                                                                             100.3                                       I     22.9     22.9     Si.sup.1 -20 wt % Al.sup.4                                                              125.5                                       J      4.9     44.5     Si-20 wt % Al                                                                           128.3                                       ______________________________________                                         .sup.1 Alfa Products, Division of Johnson Matthey Co., Ward Hill, MA          .sup.2 Superstrong MCA, Norton Co., Worcester, MA, 500 grit                   .sup.3 Atlantic Equipment Engineers, Bergenfield, NJ, -325 mesh               .sup.4 AESAR Group of Johnson Matthey Co., Seabrook, NH, 99.9% pure, 2-10     mm granules                                                              

A master particulate admixture comprising by weight about 75 grams ofALFA® molybdenum particulate (Alfa Products, Division of Johnson MattheyCo., Ward Hill, Mass.) and about 75 grams of Superstrong NCA siliconcarbide particulate (Norton Company, Worcester, Mass.) was prepared byloading the particulates into a jar mill and roll mixing in the absenceof grinding media for about 1 hour. For all except the Sample Fexperimental run, the composition of each permeable mass of filler wasformulated by "diluting" down a particular quantity of the master blendwith additional superstrong MCA silicon carbide particulate,specifically, by adding the desired quantity of silicon carbide to thedesired quantity of the master blend and roll mixing for about 15minutes in substantially the same manner as was used to mix the masterblend.

The permeable mass comprising the particulate admixture of molybdenumand silicon carbide was then poured into a Grade ATJ graphite crucible(Union Carbide Company, Carbon Products Division, Cleveland, Ohio)measuring about 2 inches (51 mm) square by about 2.5 inches (64 mm) inheight and leveled. The graphite crucible and its contents were thentapped by hand several times to consolidate the powder somewhat bycollapsing any excessive pore space between the particles in thepermeable mass. The desired quantity of parent metal particulate orgranules were then poured on top of the permeable mass and leveled tocomplete the lay-up.

Each lay-up was then placed into the vacuum chamber of a vacuum furnaceat a temperature of about 20° C. The vacuum chamber was sealed and thecontents of the vacuum chamber were twice evacuated to about 2×10-4 torrand backfilled with commercially pure argon gas to about atmosphericpressure. After the second backfill, an argon gas flow through thevacuum chamber was established and maintained at a flow rate of about1000sccm at a pressure above atmospheric pressure of about 5 psi (35,000Pa).

The temperature of the vacuum chamber and its contents was thenincreased from a temperature of about 20° C. to a temperature of about1700° C. at a rate of about 400° C. per hour. After maintaining atemperature of about 1700° C. for about 10 hours, the temperature of thevacuum chamber and its contents was then decreased to about 20° C. at arate of about 400° C. per hour. When the temperature inside the vacuumchamber had cooled down to substantially ambient temperature (e.g.,about 200° C.), the pressure in the vacuum chamber was equilibrated withthe ambient atmospheric pressure, the furnace chamber was opened, andthe lay-ups for Samples F-J were removed from the vacuum chamber anddisassembled.

Disassembly of each lay-up revealed the formation of a composite body.Specifically, it appeared that each permeable mass had beensubstantially completely infiltrated. Each composite body was sectionedwith a diamond saw, mounted in plastic and polished with progressivelyfiner grades of diamond polishing compound in preparation formicroscopic examination. Each formed composite body Was also analyzedqualitatively using x-ray diffraction substantially in accordance withExample 1.

FIGS. 10A and 10B are a scanning electron photomicrograph usingbackscattered electron imaging and an optical photomicrograph taken atabout 50× and about 106× magnification, respectively, of a polishedcross section of the Sample F composite material.

FIG. 11 is an optical photomicrograph taken at about 106× magnificationof a polished cross section of the Sample G composite material.

FIG. 12 is an optical photomicrograph taken at about 106× magnificationof a polished cross section of the Sample H composite material.

FIGS. 13A and 13B are optical photomicrographs taken at about 53× and425× magnification, respectively, of a polished cross section of theSample I composite material.

FIG. 14 is an optical photomicrograph taken at about 106× magnificationof a polished cross section of the Sample J composite material.

The qualitative X-ray diffraction analyses of the Sample F, G and Hcomposite materials revealed the presence of the following phases ineach composite body: Si, SiC and MoSi₂. Similar analyses of the Sample Iand J composite materials additionally revealed the presence of an Alphase in the formed composite body.

Thus, this Example demonstrates that a composite body comprising anMoSi₂ molybdenum disilicide intermetallic oxidation reaction product canbe formed by reactively infiltrating a parent metal comprising siliconor a silicon-aluminum alloy into a permeable mass comprising molybdenum.

We claim:
 1. A method for producing a self-supporting body comprising infiltrating a permeable mass with an oxidation reaction product obtained by oxidation of a parent metal to form a polycrystalline material comprising (i) at least one oxidation reaction product of said parent metal with at least one solid-phase oxidant, and (ii) a metallic component comprising at least one metallic phase, said method comprising the steps of:(a) forming a permeable mass comprising an oxidant consisting essentially of at least one solid-phase oxidant selected from the group consisting of the halogens, sulphur and its compounds, metals, metal oxides other than the silicates, and metal nitrides other than those of boron and silicon; (b) orienting said permeable mass and a source of said parent metal relative to each other so that formation of said at least one oxidation reaction product will occur into said permeable mass; (c) heating said source of parent metal to a temperature above the melting point of said parent metal but below the melting point of said at least one oxidation reaction product to form a body of molten parent metal; (d) reacting said body of molten parent metal with said at least one solid-phase oxidant at said temperature to permit said at least one oxidation reaction product to form; (e) maintaining at least a portion of said at least one oxidation reaction product in contact with and between said molten parent metal and said at least one solid-phase oxidant at said temperature to progressively draw molten parent metal through said at least one oxidation reaction product towards said at least one solid-phase oxidant to permit fresh oxidation reaction product to continue to form at an interface between said at least one solid-phase oxidant and previously formed oxidation reaction product that has infiltrated said permeable mass; and (f) continuing step (e) at said temperature for a time sufficient to infiltrate at least a portion of said permeable mass with said polycrystalline material, thereby forming said self-supporting body comprising (a) said at least one oxidation reaction product; and (b) a metallic component comprising at least one metallic phase.
 2. The method of claim 1, wherein said permeable mass further comprises at least one second or foreign metal.
 3. A method for producing a self-supporting composite body comprising infiltrating a permeable mass with a polycrystalline material comprising at least one oxidation reaction product, said method comprising the steps of:(a) forming a permeable mass comprising at least one filler material and at least one solid-phase oxidant selected from the group consisting of the halogens, sulphur and its compounds, metals, metal oxides and metal nitrides other than boron nitride; (b) orienting said permeable mass and a source of said parent metal relative to each other so that formation of said oxidation reaction product of said parent metal and said at least one solid-phase oxidant will occur into said permeable mass; (c) heating said source of parent metal to a temperature above the melting point of said parent metal but below the melting point of said oxidation reaction product to form a body of molten parent metal; (d) reacting said body of molten parent metal with an oxidant consisting essentially of said at least one solid-phase oxidant at said temperature to permit said at least one oxidation reaction product to form; (e) maintaining at least a portion of said at least one oxidation reaction product in contact with and between said molten parent metal and said at least one solid-phase oxidant to progressively draw molten parent metal through said at least one oxidation reaction product toward said at least one solid-phase oxidant and towards and into the permeable mass of filler material to permit fresh oxidation reaction product to continue to form at an interface between said at least one solid-phase oxidant and previously formed oxidation reaction product that has infiltrated said permeable mass; and (f) continuing step (e) at said temperature for a time sufficient to infiltrate at least a portion of said permeable mass with said polycrystalline material, thereby forming said self-supporting composite body comprising said at least one oxidation reaction product and said at least one filler material embedded by said at least one oxidation reaction product.
 4. The method of claim 3, wherein said at least one oxidation reaction product comprises at least one phase selected from the group consisting of art intermetallic phase and a ceramic phase.
 5. The method of claim 3, wherein said polycrystalline material further comprises a metallic component comprising at least one metallic constituent.
 6. The method of claim 5, wherein said at least one metallic constituent comprises at least one constituent selected from the group consisting of at least one residual unreacted constituent of said parent metal and at least one second or foreign metal.
 7. The method of claim 3, wherein said parent metal comprises aluminum, said solid-phase oxidant comprises niobium and said oxidation reaction product comprises niobium aluminide (NbAl₃).
 8. The method of claim 3, wherein said parent metal comprises aluminum, said solid-phase oxidant comprises titanium and said oxidation reaction product comprises titanium aluminide (TiAl₃).
 9. The method of claim 3, wherein said parent metal comprises titanium, said solid-phase oxidant comprises aluminum nitride and said oxidation reaction product comprises at least one titanium aluminide intermetallic phase.
 10. The method of claim 3, wherein said parent metal comprises silicon, said solid-phase oxidant comprises molybdenum and said oxidation reaction product comprises molybdenum disilicide.
 11. The method of claim 3, wherein said filler material comprises at least one material selected from the group consisting of silicon carbide and titanium diboride.
 12. The method of claim 1, wherein said parent metal comprises at least one metal selected from the group consisting of aluminum, silicon, titanium, zirconium, hafnium, tin and zinc.
 13. The method of claim 1, wherein said solid-phase oxidant comprises at least one material selected from the group consisting of arsenic, selenium, tellurium, molybdenum, niobium, titanium and silicon.
 14. The method of claim 1, wherein said at least one metallic phase comprises at least one intermetallic phase.
 15. The method of claim 1, wherein said permeable mass further comprises at least one filler material.
 16. The method of claim 1, wherein said metal oxides comprise at least one oxide selected from the group consisting of the oxides of chromium, molybdenum, niobium and silicon.
 17. The method of claim 3, wherein said metal nitrides comprise a nitride of at least one metal selected from the group consisting of aluminum and silicon.
 18. The method of claim 3, wherein said at least one oxidation reaction product comprises at least two oxidation reaction products comprising at least one intermetallic phase and at least one ceramic phase.
 19. The method of claim 6, wherein said at least one second or foreign metal comprises a metal reduced from said at least one solid-phase oxidant.
 20. A method for producing a self-supporting composite body comprising infiltrating a permeable mass with a polycrystalline material comprising at least one oxidation reaction product comprising an intermetallic material, said method comprising the steps of:(a) forming a permeable mass comprising at least one solid-phase oxidant selected from the group consisting of borides, carbides, nitrides, oxides and metals; (b) orienting said permeable mass and a source of a parent metal relative to each other so that formation of said at least one oxidation reaction product of said parent metal and said at least one solid-phase oxidant will occur into said permeable mass; (c) heating said source of parent metal to a temperature above the melting point of said parent metal but below the melting point of said oxidation reaction product to form a body of molten parent metal; (d) reacting said body of molten parent metal with an oxidant consisting essentially of said at least one solid-phase oxidant at said temperature to permit said at least one oxidation reaction product comprising said intermetallic material to form; (e) maintaining at least a portion of said at least one oxidation reaction product in contact with and between said molten parent metal and said at least one solid-phase oxidant to progressively draw molten parent metal through said at least one oxidation reaction product toward said at least one solid-phase oxidant and towards and into the mass of filler material to permit fresh oxidation reaction product to continue to form at an interface between said at least one solid-phase oxidant and previously formed oxidation reaction product that has infiltrated said permeable mass; and (f) continuing step (e) at said temperature for a time sufficient to infiltrate at least a portion of said permeable mass with said polycrystalline material, thereby forming said self-supporting composite body comprising said at least one oxidation reaction product comprising said intermetallic material.
 21. The method of claim 20, wherein said intermetallic material comprises at least one member selected from the group consisting of a metal silicide and a metal aluminide. 